Production of ammonium nitrate charges



W WW3 W. R. DAWS mwm PRODUCTION OF AMMONIUM NITRATE CHARGES Filed Jan. 15 194:8

inventov" WALTER ROWDEN DAVIS Patented May 30, 1950 PRODUCTION OF AMMONIUM NITRATE CHARGES Walter Rowden. Davis, Hitchin, England, assignor to Imperial Chemical Industries Limited, a corporation of Great Britain Application January 15, 1948, Serial No. 2,463 In Great Britain February 7, 1947 6 Claims.

The present invention relates to the production of ammonium nitrate charges and is particularly concerned with the production of ammonium nitrate charges in compact form and suitable for the generation of gas pressure.

In British specification No. 570,075 there is described and claimed inter alia a process for the production of combustible charges in compact form and suitable for the generation of gas pressure by at least partially fusing an ammonium nitrate charge and casting the same at a temperature not exceeding 115 C., and preferably not exceeding 110 C., the said charge containing ammonium nitrate, an oxidisable material, a chromate compound capable of sensitising the thermal decomposition of ammonium nitrate, and at least one ammonium nitrate fusion promoting ingredient solid at ordinary temperature, in amount suficient to render the charge pourable at a temperature not exceeding 115 C. and preferably not exceeding 110 C. Preferably, it is stated, the chromate compound is introduced into the composition only after a mixture at a temperature at least approximating to pouring temperature has been formed, comprising at least the ammonium nitrate and the fusion promoting ingredients. It is also stated that the maintenance of compositions containing chromate compound at high temperature should be avoided by casting the composition without unnecessary delay, otherwise it may show evidence of exothermic reaction.

We have now ascertained that at temperature close to solidification these compositions do not crystallise as a whole, but some of the ingredients separate out before the others. For this reason and because the compositions do not remain stable indefinitely in the molten state but darken and evolve gas, difficulties are encountered when attempts are made to produce sound and uniform casts having a thickness greater than about an inch.

It has now been found that highly satisfactory ammonium nitrate charges of the kind comprising one or more fusion promoting ingredients and a chromate compound sensitiser of thermal decomposition for the ammonium nitrate can be formed in compact form and if desired of large diameter or large web thickness in a simple and convenient manner by gradually building a solid deposit of the required thickness upon a rotating mandrel which at the beginning of the deposition is partially immersed in and as deposition proceeds is slowly distanced from a molten ammonium nitrate composition, at a temperature sufiiciently low to prevent its decomposition and sufliciently above the temperature at which crystals begin to be deposited from the melt, of uniform composition throughout, and kept at a constant level in a shallow bath.

As examples of a chromate compound sensitiser of thermal decomposition of ammonium nitrate are: ammonium bichromate; potassium bichromate; potassium chromate.

According to the present invention, therefore, the process for the production of ammonium nitrate charges of the aforesaid kind comprises gradually building a solid deposit of the required thickness upon a rotating mandrel which at the beginning of the deposition is partially immersed in and as deposition proceeds is slowly distanced from a molten ammonium nitrate composition at a temperature sufiiciently low to prevent its decomposition and sufiiciently above the temperature at which crystals begin to be deposited from the melt, of uniform composition throughout, and kept at a constant level in a shallow bath.

Preferably the mandrel is a slightly tapered cylindrical steel mandrel to facilitate its withdrawal from the completed casting. It is most desirable to control the speed of rotation of the mandrel, and the rate of cooling of the deposit thereon for instance by directing upon its surface a current of cool air. Furthermore the shallow bath is preferably replenished at fairly frequent intervals with the already molten heat sensitive ammonium nitrate composition which is preferably not allowed to remain too long after its preparation in the molten condition thereby minimising any tendency to decomposition in the melt.

Preferably the thickness of each layer deposited is of the order of /20'0 inch and the time for making a charge of six inches web thickness on a, six and a half inches diameter mandrel is about eight hours. The control of the thickness of the layers of melt deposited is preferably effected by a doctor knife provided in the shallow bath. Currents of cold air may be directed upon the deposit to accelerate its rate of cooling.

It is possible to employ as a mandrel a cylinder turned from a previously made annular charge of ammonium nitrate of identical composition to that of the melt from which deposition is to take place thereby permitting solid, 1. e. non-annular charges to be produced of the same composition throughout.

The invention is illustrated by the following example, in which the parts are parts by weight, and with reference to the diagrammatic drawing accompanying the specification illustrating a sectional elevation of apparatus suitable for carrying out the process of the invention.

Example In Figure 1, l is a jacketed vessel provided with a stirrer 2 and a branched discharge tube 3, having branches 4 and 4' controlled by cocks 5 and 5 respectively. In vessel l a mixture consisting of ammonium nitrate 69.6 parts, sodium nitrate 13.3 parts, guanidine nitrate 5.4 parts, potassium nitrate 7.6 parts, magnesium nitrate 1.1 parts is introduced and heated to 115 C. and stirred at this temperature until the whole of the material has been fused. Branch tube 5 leads into a jacketed vessel 6 which is provided with a stirrer I and a discharge pipe 8 having a cock 9 and leading into a jacketed tank 19. Branch tube 5 leads into a jacketed vessel 6' which is provided with a stirrer l and a discharge pipe 8' having a cock 9 and leading into the tank l9 likewise. The jacketed vessel l is ten timeslarger than each of the-jacketed vessels 6 and 6'. A stipulated quantity of the fused salt from the vessel l is delivered into vessel 9 and 8 parts of ammonium bicromate are added to 92 parts of the fused melt introduced. 0.8 part of Water is also added. The temperature is kept at 115 C. in vessel 6. At the same time a similar ammonium nitrate melt containing ammonium bicromate is prepared in vessel 6. The scum formed on the melts in vesselsfi-"and' 5 areremoved and without unnecessary delay the ammonium bichromate containing melt, prepared in vessels 6 and ii are delivered into the tank It at one end of which there is provided a circulating pump II and at the central portion of which there is provided a shallow constant level dipping tank l2 provided with a Weir 57 at one end and a weir 8 at the other end thereof. The melt in tanks l ll and i2 is heated by the circulation of hot oil in chamber [9 and in the jacket 29 of vessel [0. The two vessels 6 and B are provided in order to reduce the time taken forthe initial filling of vessel It). As the quantity of the melt diminishes in tank It during the dipping'operation it is only necessary to use one of the vessels 5 and- 6 for the preparation of further quantities of melt in order to replenish tank I0. Conditions are so arranged that the melt in tanks l9 and I2 is kept constantly in circulation. The level of liquid in tank l0 drops as the melt is used up,- from tank 12. The level of liquid in the tank 1.2 1s kept constant due to the circulation of the liquid by the circulating pump I l, with return flow over theweir 18. The tank 12 is provided with a doctor knife 13 and a six anda half inch diameter mandrel l4 adapted to rotate and which is arranged to dip into the melt in tank l2 and to be gradually withdrawn by the mechanism l5 at such a rate that the deposit l6 increased in thickness by /200 inch at each revolution of the mandrel. The time for making a charge of six inch web thickness on the six and a half inch diameter mandrel I4 is about eight hours.

I claim:

1. A process for the production of ammonium nitrate charges which comprises partially immersing a rotating mandrel in a constant level shallow bath of a uniform molten ammonium nitrate composition which is at a temperature between the decomposition temperature of the particular melt and that temperature at which crystals of the composition are deposited from the melt, and slowly distancing the mandrel from the said bath as deposition of the composition in layers on the mandrel occurs thus uniformly forming a solid deposit of a required thickness on the said mandrel.

2. A process as set forth in claim 1 wherein.

the said mandrel is a slightly tapered cylindrical steel mandrel.

3. A process as set forth in claim 1 wherein the said mandrel is a cylinder of ammonium nitrate of identical composition as that of the melt from which deposition is to take place.

4. A process as set forth in claim 1 wherein the speed of rotation of themandrel and the rate of distancing the mandrel from the said bath controls the deposition of said charge on REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,225,091 Whitcome V May 8, 1917 1,717,236 MacMenigall June 11, 1929 1,777,648 McKay et al Oct. 7, 1930 1,969,071 Glidden et al. Aug. 7, 1934 2,133,947 Boecler Oct. 25, 1938' 2,335,722 Adams n-. Nov. 30, 1943 

1. A PROCESS FOR THE PRODUCTION OF AMMONIUM NITRATE CHARGES WHICH COMPRISES PARTIALLY IMMERSING A ROTATING MANDREL IN A CONSTANT LEVEL SHALLOW BATH OF A UNIFORM MOLTEN AMMONIUM NITRATE COMPOSITION WHICH IS AT A TEMPERATURE BETWEEN THE DECOMPOSITION TEMPERATURE OF THE PARTICULAR MELT AND THAT TEMPERATURE AT WHICH CRYSTALS OF THE COMPOSITION ARE DEPOSITED FROM THE MELT, AND SLOWLY DISTANCING THE MANDREL FROM THE SAID BATH AS DEPOSITION OF THE COMPOSITION IN LAYERS ON THE MANDREL OCCURS THUS UNIFORMLY FORMING A SOLID DEPOSIT OF A REQUIRED THICKNESS ON THE SAID MANDREL. 